Java tutorial
/* * Copyright (C) 2006 The Guava Authors * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package com.google.common.util.concurrent; import static com.google.common.base.Preconditions.checkArgument; import static com.google.common.base.Preconditions.checkNotNull; import com.google.common.annotations.Beta; import com.google.common.collect.ObjectArrays; import com.google.common.collect.Sets; import java.lang.reflect.InvocationHandler; import java.lang.reflect.InvocationTargetException; import java.lang.reflect.Method; import java.lang.reflect.Proxy; import java.util.Set; import java.util.concurrent.Callable; import java.util.concurrent.ExecutionException; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Future; import java.util.concurrent.TimeUnit; import java.util.concurrent.TimeoutException; /** * A TimeLimiter that runs method calls in the background using an * {@link ExecutorService}. If the time limit expires for a given method call, * the thread running the call will be interrupted. * * @author Kevin Bourrillion * @since 1.0 */ @Beta public final class SimpleTimeLimiter implements TimeLimiter { private final ExecutorService executor; /** * Constructs a TimeLimiter instance using the given executor service to * execute proxied method calls. * <p> * <b>Warning:</b> using a bounded executor * may be counterproductive! If the thread pool fills up, any time callers * spend waiting for a thread may count toward their time limit, and in * this case the call may even time out before the target method is ever * invoked. * * @param executor the ExecutorService that will execute the method calls on * the target objects; for example, a {@link * Executors#newCachedThreadPool()}. */ public SimpleTimeLimiter(ExecutorService executor) { this.executor = checkNotNull(executor); } /** * Constructs a TimeLimiter instance using a {@link * Executors#newCachedThreadPool()} to execute proxied method calls. * * <p><b>Warning:</b> using a bounded executor may be counterproductive! If * the thread pool fills up, any time callers spend waiting for a thread may * count toward their time limit, and in this case the call may even time out * before the target method is ever invoked. */ public SimpleTimeLimiter() { this(Executors.newCachedThreadPool()); } @Override public <T> T newProxy(final T target, Class<T> interfaceType, final long timeoutDuration, final TimeUnit timeoutUnit) { checkNotNull(target); checkNotNull(interfaceType); checkNotNull(timeoutUnit); checkArgument(timeoutDuration > 0, "bad timeout: %s", timeoutDuration); checkArgument(interfaceType.isInterface(), "interfaceType must be an interface type"); final Set<Method> interruptibleMethods = findInterruptibleMethods(interfaceType); InvocationHandler handler = new InvocationHandler() { @Override public Object invoke(Object obj, final Method method, final Object[] args) throws Throwable { Callable<Object> callable = new Callable<Object>() { @Override public Object call() throws Exception { try { return method.invoke(target, args); } catch (InvocationTargetException e) { throwCause(e, false); throw new AssertionError("can't get here"); } } }; return callWithTimeout(callable, timeoutDuration, timeoutUnit, interruptibleMethods.contains(method)); } }; return newProxy(interfaceType, handler); } // TODO: should this actually throw only ExecutionException? @Override public <T> T callWithTimeout(Callable<T> callable, long timeoutDuration, TimeUnit timeoutUnit, boolean amInterruptible) throws Exception { checkNotNull(callable); checkNotNull(timeoutUnit); checkArgument(timeoutDuration > 0, "timeout must be positive: %s", timeoutDuration); Future<T> future = executor.submit(callable); try { if (amInterruptible) { try { return future.get(timeoutDuration, timeoutUnit); } catch (InterruptedException e) { future.cancel(true); throw e; } } else { return Uninterruptibles.getUninterruptibly(future, timeoutDuration, timeoutUnit); } } catch (ExecutionException e) { throw throwCause(e, true); } catch (TimeoutException e) { future.cancel(true); throw new UncheckedTimeoutException(e); } } private static Exception throwCause(Exception e, boolean combineStackTraces) throws Exception { Throwable cause = e.getCause(); if (cause == null) { throw e; } if (combineStackTraces) { StackTraceElement[] combined = ObjectArrays.concat(cause.getStackTrace(), e.getStackTrace(), StackTraceElement.class); cause.setStackTrace(combined); } if (cause instanceof Exception) { throw (Exception) cause; } if (cause instanceof Error) { throw (Error) cause; } // The cause is a weird kind of Throwable, so throw the outer exception. throw e; } private static Set<Method> findInterruptibleMethods(Class<?> interfaceType) { Set<Method> set = Sets.newHashSet(); for (Method m : interfaceType.getMethods()) { if (declaresInterruptedEx(m)) { set.add(m); } } return set; } private static boolean declaresInterruptedEx(Method method) { for (Class<?> exType : method.getExceptionTypes()) { // debate: == or isAssignableFrom? if (exType == InterruptedException.class) { return true; } } return false; } // TODO: replace with version in common.reflect if and when it's open-sourced private static <T> T newProxy(Class<T> interfaceType, InvocationHandler handler) { Object object = Proxy.newProxyInstance(interfaceType.getClassLoader(), new Class<?>[] { interfaceType }, handler); return interfaceType.cast(object); } }